title: Single doses of THC and cocaine decrease proficiency of impulse control in heavy cannabis users.
abstract: OBJECTIVE
  Cannabis is the most popular drug used in the European Union, closely followed by cocaine. Whereas cannabis impairs neurocognitive function in occasional cannabis users, such impairments appear less prominent in heavy users, possibly as a result of tolerance. The present study was designed to assess whether the impairing effects of Δ(9) -tetrahydrocannabinol (THC) in heavy cannabis users would present in a wide range of neuropsychological functions or selectively affect specific performance domains. We also assessed the acute effects of cocaine on neurocognitive functions of heavy cannabis users.
  
  
  METHODS
  Heavy cannabis users, who had a history of cocaine use (n = 61), participated in a double-blind, placebo-controlled, three-way crossover study. Subjects received single doses of cocaine HCl (300 mg), cannabis (THC μg·kg(-1) ) and placebo, and completed a number of tests measuring impulse control and psychomotor function.
  
  
  RESULTS
  Single doses of cannabis impaired psychomotor function and increased response errors during impulsivity tasks. Single doses of cocaine improved psychomotor function and decreased response time in impulsivity tasks, but increased errors.
  
  
  CONCLUSIONS
  Heavy cannabis users display impairments in a broad range of neuropsychological domains during THC intoxication. Impairments observed in psychomotor tasks, but not in impulsivity tasks, appeared smaller in magnitude as compared with those previously reported in occasional cannabis users. Heavy cannabis users were sensitive to the stimulating and inhibitory effects of cocaine on psychomotor function and impulsivity respectively. The reduction in proficiency in impulse control may put drug users at increased risk of repeated drug use and addiction.
authors.affiliation: Department Neuropsychology and Psychopharmacology, Faculty of Psychology and Neuroscience, Maastricht University, Maastricht, The Netherlands.
authors.forename: J H P
authors.initials: JH
authors.lastname: van Wel
authors.forename: K P C
authors.initials: KP
authors.lastname: Kuypers
authors.forename: E L
authors.initials: EL
authors.lastname: Theunissen
authors.forename: S W
authors.initials: SW
authors.lastname: Toennes
authors.forename: D B
authors.initials: DB
authors.lastname: Spronk
authors.forename: R J
authors.initials: RJ
authors.lastname: Verkes
authors.forename: J G
authors.initials: JG
authors.lastname: Ramaekers
mesh_terms: D000280:Administration, Inhalation; D000284:Administration, Oral; D000328:Adult; D000697:Central Nervous System Stimulants / Q000008:administration & dosage* / Q000493:pharmacokinetics; D003042:Cocaine / Q000008:administration & dosage* / Q000493:pharmacokinetics; D019970:Cocaine-Related Disorders / Q000523:psychology*; D003071:Cognition / Q000187:drug effects; D018592:Cross-Over Studies; D004311:Double-Blind Method; D013759:Dronabinol / Q000008:administration & dosage* / Q000493:pharmacokinetics; D005260:Female; D006213:Hallucinogens / Q000008:administration & dosage* / Q000493:pharmacokinetics; D006801:Humans; D007175:Impulsive Behavior / Q000523:psychology*; D008297:Male; D002189:Marijuana Abuse / Q000523:psychology*; D008385:Marijuana Smoking / Q000523:psychology*; D009483:Neuropsychological Tests; D011597:Psychomotor Performance / Q000187:drug effects; D011930:Reaction Time / Q000187:drug effects; D013997:Time Factors; D055815:Young Adult
chemical_list: D000697:Central Nervous System Stimulants; D006213:Hallucinogens; D013759:Dronabinol; D003042:Cocaine
keywords: addiction; cannabis; cocaine; cross-tolerance; impulsivity; tolerance